In recent years, a pre-filled syringe has been developed: functioning as a container capable of containing a medical drug and a liquid drug in advance required for medical treatments by ensuring stability during storage of the medical drug and the liquid drug; and also functioning an injection syringe during use.
For example, Japanese Patent Laying-Open No. 2007-185319 (PTD 1) discloses such a pre-filled syringe.
The pre-filled syringe disclosed in PTD 1 includes: a cylindrical portion having a front end and a rear end that are opened; a nozzle portion attached to the front end of the cylindrical portion and having a discharge path; a front end-side gasket, an intermediate gasket and a rear end-side gasket provided on the front end side, the intermediate portion and the rear end side, respectively, of the cylindrical portion so as to freely slide inside the cylindrical portion; and a plunger capable of pushing the rear end-side gasket toward the front end. A medical drug is contained in a front chamber provided inside the cylindrical portion and located between the front end-side gasket and the intermediate gasket. A liquid drug is contained in a rear chamber provided inside the cylindrical portion and located between the intermediate gasket and the rear end-side gasket.
In the state where the plunger is not pushed in, the nozzle portion and the front chamber are maintained in a liquid-tight state by the front end-side gasket; the front chamber and the rear chamber are maintained in a liquid-tight state by the intermediate gasket; and the rear chamber is maintained in a liquid-tight state also by the rear end-side gasket.
The cylindrical portion is provided with a bypass portion bulging in its radial direction, and the intermediate gasket has an outer circumferential surface provided with a groove portion. In the state where the bypass portion and the groove portion face each other, the front chamber and the rear chamber are brought into communication with each other.
Furthermore, the nozzle portion has a housing portion capable of housing the front end-side gasket on the side at which this nozzle portion is attached to the cylindrical portion. When the front end-side gasket moves to the housing portion, the discharge path and the front chamber are brought into communication with each other through a space provided between the circumferential surface of the front end-side gasket and the nozzle portion.
When the plunger is pushed toward the front end of the cylindrical portion, the front end-side gasket, the intermediate gasket and the rear end-side gasket move toward the front end. In this case, the front end-side gasket moves to the nozzle portion, thereby allowing communication between the discharge path and the front chamber, and also causing the groove portion of the intermediate gasket and the bypass portion of the cylindrical portion to face each other, so that the front chamber and the rear chamber communicate with each other through the groove portion and the bypass portion.
In the state where the front chamber and the rear chamber communicate with each other, a liquid drug is pushed forward by the rear end-side gasket, so that the liquid drug contained in the rear chamber is moved to the front chamber and mixed with the medical drug, thereby preparing a liquid mixture. By further pushing the plunger in the state where the liquid mixture is prepared, the intermediate gasket pushed into the rear end-side gasket moves toward the front end, so that the liquid mixture is pushed into the nozzle portion by the intermediate gasket. Thereby, the liquid mixture is discharged through the discharge path to the outside.